Johnson, who received a kidney from his 25-year-old son Daniel, is in fair condition, officials said in a news release. Johnson's vital signs are stable, and he is comfortable and conscious. Daniel, who underwent a simultaneous surgery, is in good condition as well, officials said.

"Everything went smoothly and as expected for both donor and recipient," hospital officials said in a statement.

Johnson, who turned 57 in July, was his son's age when he was diagnosed with glomerulonephritis, an acute inflammation of the kidney.

The superintendent arrived at the hospital before 6 a.m. Wednesday for the surgery, and told reporters gathered that he was "anxious to get it over with" and that he was proud of his son "for stepping up."

Johnson has previously talked about how awed he was by his son's impending donation, as well as the kindness of numerous people who came forward to see if their kidneys may be a match for his. He also talked about his hope for a healthier future.

"It's a sense of relief because, let's face it, as my kidneys (decline), then my only alternative is dialysis for the rest of my life, which I really don't want to do," Johnson previously said of the surgery. "When your child is doing it for you, it means a little bit more."

To prepare for the surgery, both father and son had to shed pounds and make healthier eating choices. Each began dieting and exercising more regularly.

Daniel, a former football player and track and field athlete at Knox College in Galesburg, Ill., was told by doctors that he had to lose 15 pounds in order to have the surgery. He said he spent close to two hours a day on cardiovascular exercise, including working out in a gym and running along the lakefront with friends.

But it proved unnecessary when son Daniel stepped forward, learned his own kidney...

Chicago police Superintendent Eddie Johnson says he couldn't bring himself to follow doctors' advice earlier this year to seek out donors when his kidneys were suddenly functioning at less than 10 percent capacity.

But it proved unnecessary when son Daniel stepped forward, learned his own kidney...

(Jeremy Gorner and Marwa Eltagouri)

Johnson found out about the disease during a doctor's visit as part of his application process to become a Chicago police officer. At the time of his diagnosis, doctors thought his kidneys would last only four or five years.

Johnson first went public about being on the waiting list for a kidney in late January after nearly fainting during a news conference while flanked by Mayor Rahm Emanuel and other police officials. He said he had told Emanuel about the health issue last year when the mayor was considering him to be superintendent, a surprise choice since Johnson had not applied for the job.

Johnson told a Tribune reporter Tuesday that he would likely remain in the hospital for three to five days, while his son recovers there for one or two days.

Rush officials said the operations were performed by Dr. Martin Hertl and Dr. Edward Hollinger and their surgical teams. Officials said they would update the superintendent's condition at 11 a.m. Thursday morning.